// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 *  Copyright (C) 2017 Zihao Yu
 */

#include <linux/elf.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/hashtable.h>
#include <linux/kernel.h>
#include <linux/log2.h>
#include <linux/moduleloader.h>
#include <linux/sizes.h>
#include <linux/pgtable.h>
#include <asm/alternative.h>
#include <asm/sections.h>

struct used_bucket {
        struct list_head head;
        struct hlist_head *bucket;
};

struct relocation_head {
        struct hlist_node node;
        struct list_head rel_entry;
        void *location;
};

struct relocation_entry {
        struct list_head head;
        Elf_Addr value;
        unsigned int type;
};

struct relocation_handlers {
        int (*reloc_handler)(struct module *me, void *location, Elf_Addr v);
        int (*accumulate_handler)(struct module *me, void *location,
                                  long buffer);
};

/*
 * The auipc+jalr instruction pair can reach any PC-relative offset
 * in the range [-2^31 - 2^11, 2^31 - 2^11)
 */
static bool riscv_insn_valid_32bit_offset(ptrdiff_t val)
{
#ifdef CONFIG_32BIT
        return true;
#else
        return (-(1L << 31) - (1L << 11)) <= val && val < ((1L << 31) - (1L << 11));
#endif
}

static int riscv_insn_rmw(void *location, u32 keep, u32 set)
{
        __le16 *parcel = location;
        u32 insn = (u32)le16_to_cpu(parcel[0]) | (u32)le16_to_cpu(parcel[1]) << 16;

        insn &= keep;
        insn |= set;

        parcel[0] = cpu_to_le16(insn);
        parcel[1] = cpu_to_le16(insn >> 16);
        return 0;
}

static int riscv_insn_rvc_rmw(void *location, u16 keep, u16 set)
{
        __le16 *parcel = location;
        u16 insn = le16_to_cpu(*parcel);

        insn &= keep;
        insn |= set;

        *parcel = cpu_to_le16(insn);
        return 0;
}

static int apply_r_riscv_32_rela(struct module *me, void *location, Elf_Addr v)
{
        if (v != (u32)v) {
                pr_err("%s: value %016llx out of range for 32-bit field\n",
                       me->name, (long long)v);
                return -EINVAL;
        }
        *(u32 *)location = v;
        return 0;
}

static int apply_r_riscv_64_rela(struct module *me, void *location, Elf_Addr v)
{
        *(u64 *)location = v;
        return 0;
}

static int apply_r_riscv_branch_rela(struct module *me, void *location,
                                     Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u32 imm12 = (offset & 0x1000) << (31 - 12);
        u32 imm11 = (offset & 0x800) >> (11 - 7);
        u32 imm10_5 = (offset & 0x7e0) << (30 - 10);
        u32 imm4_1 = (offset & 0x1e) << (11 - 4);

        return riscv_insn_rmw(location, 0x1fff07f, imm12 | imm11 | imm10_5 | imm4_1);
}

static int apply_r_riscv_jal_rela(struct module *me, void *location,
                                  Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u32 imm20 = (offset & 0x100000) << (31 - 20);
        u32 imm19_12 = (offset & 0xff000);
        u32 imm11 = (offset & 0x800) << (20 - 11);
        u32 imm10_1 = (offset & 0x7fe) << (30 - 10);

        return riscv_insn_rmw(location, 0xfff, imm20 | imm19_12 | imm11 | imm10_1);
}

static int apply_r_riscv_rvc_branch_rela(struct module *me, void *location,
                                         Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u16 imm8 = (offset & 0x100) << (12 - 8);
        u16 imm7_6 = (offset & 0xc0) >> (6 - 5);
        u16 imm5 = (offset & 0x20) >> (5 - 2);
        u16 imm4_3 = (offset & 0x18) << (12 - 5);
        u16 imm2_1 = (offset & 0x6) << (12 - 10);

        return riscv_insn_rvc_rmw(location, 0xe383,
                        imm8 | imm7_6 | imm5 | imm4_3 | imm2_1);
}

static int apply_r_riscv_rvc_jump_rela(struct module *me, void *location,
                                       Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u16 imm11 = (offset & 0x800) << (12 - 11);
        u16 imm10 = (offset & 0x400) >> (10 - 8);
        u16 imm9_8 = (offset & 0x300) << (12 - 11);
        u16 imm7 = (offset & 0x80) >> (7 - 6);
        u16 imm6 = (offset & 0x40) << (12 - 11);
        u16 imm5 = (offset & 0x20) >> (5 - 2);
        u16 imm4 = (offset & 0x10) << (12 - 5);
        u16 imm3_1 = (offset & 0xe) << (12 - 10);

        return riscv_insn_rvc_rmw(location, 0xe003,
                        imm11 | imm10 | imm9_8 | imm7 | imm6 | imm5 | imm4 | imm3_1);
}

static int apply_r_riscv_pcrel_hi20_rela(struct module *me, void *location,
                                         Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;

        if (!riscv_insn_valid_32bit_offset(offset)) {
                pr_err(
                  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
                  me->name, (long long)v, location);
                return -EINVAL;
        }

        return riscv_insn_rmw(location, 0xfff, (offset + 0x800) & 0xfffff000);
}

static int apply_r_riscv_pcrel_lo12_i_rela(struct module *me, void *location,
                                           Elf_Addr v)
{
        /*
         * v is the lo12 value to fill. It is calculated before calling this
         * handler.
         */
        return riscv_insn_rmw(location, 0xfffff, (v & 0xfff) << 20);
}

static int apply_r_riscv_pcrel_lo12_s_rela(struct module *me, void *location,
                                           Elf_Addr v)
{
        /*
         * v is the lo12 value to fill. It is calculated before calling this
         * handler.
         */
        u32 imm11_5 = (v & 0xfe0) << (31 - 11);
        u32 imm4_0 = (v & 0x1f) << (11 - 4);

        return riscv_insn_rmw(location, 0x1fff07f, imm11_5 | imm4_0);
}

static int apply_r_riscv_hi20_rela(struct module *me, void *location,
                                   Elf_Addr v)
{
        if (IS_ENABLED(CONFIG_CMODEL_MEDLOW)) {
                pr_err(
                  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
                  me->name, (long long)v, location);
                return -EINVAL;
        }

        return riscv_insn_rmw(location, 0xfff, ((s32)v + 0x800) & 0xfffff000);
}

static int apply_r_riscv_lo12_i_rela(struct module *me, void *location,
                                     Elf_Addr v)
{
        /* Skip medlow checking because of filtering by HI20 already */
        s32 hi20 = ((s32)v + 0x800) & 0xfffff000;
        s32 lo12 = ((s32)v - hi20);

        return riscv_insn_rmw(location, 0xfffff, (lo12 & 0xfff) << 20);
}

static int apply_r_riscv_lo12_s_rela(struct module *me, void *location,
                                     Elf_Addr v)
{
        /* Skip medlow checking because of filtering by HI20 already */
        s32 hi20 = ((s32)v + 0x800) & 0xfffff000;
        s32 lo12 = ((s32)v - hi20);
        u32 imm11_5 = (lo12 & 0xfe0) << (31 - 11);
        u32 imm4_0 = (lo12 & 0x1f) << (11 - 4);

        return riscv_insn_rmw(location, 0x1fff07f, imm11_5 | imm4_0);
}

static int apply_r_riscv_got_hi20_rela(struct module *me, void *location,
                                       Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;

        /* Always emit the got entry */
        if (IS_ENABLED(CONFIG_MODULE_SECTIONS)) {
                offset = (void *)module_emit_got_entry(me, v) - location;
        } else {
                pr_err(
                  "%s: can not generate the GOT entry for symbol = %016llx from PC = %p\n",
                  me->name, (long long)v, location);
                return -EINVAL;
        }

        return riscv_insn_rmw(location, 0xfff, (offset + 0x800) & 0xfffff000);
}

static int apply_r_riscv_call_plt_rela(struct module *me, void *location,
                                       Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u32 hi20, lo12;

        if (!riscv_insn_valid_32bit_offset(offset)) {
                /* Only emit the plt entry if offset over 32-bit range */
                if (IS_ENABLED(CONFIG_MODULE_SECTIONS)) {
                        offset = (void *)module_emit_plt_entry(me, v) - location;
                } else {
                        pr_err(
                          "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
                          me->name, (long long)v, location);
                        return -EINVAL;
                }
        }

        hi20 = (offset + 0x800) & 0xfffff000;
        lo12 = (offset - hi20) & 0xfff;
        riscv_insn_rmw(location, 0xfff, hi20);
        return riscv_insn_rmw(location + 4, 0xfffff, lo12 << 20);
}

static int apply_r_riscv_call_rela(struct module *me, void *location,
                                   Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;
        u32 hi20, lo12;

        if (!riscv_insn_valid_32bit_offset(offset)) {
                pr_err(
                  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
                  me->name, (long long)v, location);
                return -EINVAL;
        }

        hi20 = (offset + 0x800) & 0xfffff000;
        lo12 = (offset - hi20) & 0xfff;
        riscv_insn_rmw(location, 0xfff, hi20);
        return riscv_insn_rmw(location + 4, 0xfffff, lo12 << 20);
}

static int apply_r_riscv_relax_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        return 0;
}

static int apply_r_riscv_align_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        pr_err(
          "%s: The unexpected relocation type 'R_RISCV_ALIGN' from PC = %p\n",
          me->name, location);
        return -EINVAL;
}

static int apply_r_riscv_add8_rela(struct module *me, void *location, Elf_Addr v)
{
        *(u8 *)location += (u8)v;
        return 0;
}

static int apply_r_riscv_add16_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u16 *)location += (u16)v;
        return 0;
}

static int apply_r_riscv_add32_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u32 *)location += (u32)v;
        return 0;
}

static int apply_r_riscv_add64_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u64 *)location += (u64)v;
        return 0;
}

static int apply_r_riscv_sub8_rela(struct module *me, void *location, Elf_Addr v)
{
        *(u8 *)location -= (u8)v;
        return 0;
}

static int apply_r_riscv_sub16_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u16 *)location -= (u16)v;
        return 0;
}

static int apply_r_riscv_sub32_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u32 *)location -= (u32)v;
        return 0;
}

static int apply_r_riscv_sub64_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u64 *)location -= (u64)v;
        return 0;
}

static int dynamic_linking_not_supported(struct module *me, void *location,
                                         Elf_Addr v)
{
        pr_err("%s: Dynamic linking not supported in kernel modules PC = %p\n",
               me->name, location);
        return -EINVAL;
}

static int tls_not_supported(struct module *me, void *location, Elf_Addr v)
{
        pr_err("%s: Thread local storage not supported in kernel modules PC = %p\n",
               me->name, location);
        return -EINVAL;
}

static int apply_r_riscv_sub6_rela(struct module *me, void *location, Elf_Addr v)
{
        u8 *byte = location;
        u8 value = v;

        *byte = (*byte - (value & 0x3f)) & 0x3f;
        return 0;
}

static int apply_r_riscv_set6_rela(struct module *me, void *location, Elf_Addr v)
{
        u8 *byte = location;
        u8 value = v;

        *byte = (*byte & 0xc0) | (value & 0x3f);
        return 0;
}

static int apply_r_riscv_set8_rela(struct module *me, void *location, Elf_Addr v)
{
        *(u8 *)location = (u8)v;
        return 0;
}

static int apply_r_riscv_set16_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u16 *)location = (u16)v;
        return 0;
}

static int apply_r_riscv_set32_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        *(u32 *)location = (u32)v;
        return 0;
}

static int apply_r_riscv_32_pcrel_rela(struct module *me, void *location,
                                       Elf_Addr v)
{
        *(u32 *)location = v - (uintptr_t)location;
        return 0;
}

static int apply_r_riscv_plt32_rela(struct module *me, void *location,
                                    Elf_Addr v)
{
        ptrdiff_t offset = (void *)v - location;

        if (!riscv_insn_valid_32bit_offset(offset)) {
                /* Only emit the plt entry if offset over 32-bit range */
                if (IS_ENABLED(CONFIG_MODULE_SECTIONS)) {
                        offset = (void *)module_emit_plt_entry(me, v) - location;
                } else {
                        pr_err("%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
                               me->name, (long long)v, location);
                        return -EINVAL;
                }
        }

        *(u32 *)location = (u32)offset;
        return 0;
}

static int apply_r_riscv_set_uleb128(struct module *me, void *location, Elf_Addr v)
{
        *(long *)location = v;
        return 0;
}

static int apply_r_riscv_sub_uleb128(struct module *me, void *location, Elf_Addr v)
{
        *(long *)location -= v;
        return 0;
}

static int apply_6_bit_accumulation(struct module *me, void *location, long buffer)
{
        u8 *byte = location;
        u8 value = buffer;

        if (buffer > 0x3f) {
                pr_err("%s: value %ld out of range for 6-bit relocation.\n",
                       me->name, buffer);
                return -EINVAL;
        }

        *byte = (*byte & 0xc0) | (value & 0x3f);
        return 0;
}

static int apply_8_bit_accumulation(struct module *me, void *location, long buffer)
{
        if (buffer > U8_MAX) {
                pr_err("%s: value %ld out of range for 8-bit relocation.\n",
                       me->name, buffer);
                return -EINVAL;
        }
        *(u8 *)location = (u8)buffer;
        return 0;
}

static int apply_16_bit_accumulation(struct module *me, void *location, long buffer)
{
        if (buffer > U16_MAX) {
                pr_err("%s: value %ld out of range for 16-bit relocation.\n",
                       me->name, buffer);
                return -EINVAL;
        }
        *(u16 *)location = (u16)buffer;
        return 0;
}

static int apply_32_bit_accumulation(struct module *me, void *location, long buffer)
{
        if (buffer > U32_MAX) {
                pr_err("%s: value %ld out of range for 32-bit relocation.\n",
                       me->name, buffer);
                return -EINVAL;
        }
        *(u32 *)location = (u32)buffer;
        return 0;
}

static int apply_64_bit_accumulation(struct module *me, void *location, long buffer)
{
        *(u64 *)location = (u64)buffer;
        return 0;
}

static int apply_uleb128_accumulation(struct module *me, void *location, long buffer)
{
        /*
         * ULEB128 is a variable length encoding. Encode the buffer into
         * the ULEB128 data format.
         */
        u8 *p = location;

        while (buffer != 0) {
                u8 value = buffer & 0x7f;

                buffer >>= 7;
                value |= (!!buffer) << 7;

                *p++ = value;
        }
        return 0;
}

/*
 * Relocations defined in the riscv-elf-psabi-doc.
 * This handles static linking only.
 */
static const struct relocation_handlers reloc_handlers[] = {
        [R_RISCV_32]            = { .reloc_handler = apply_r_riscv_32_rela },
        [R_RISCV_64]            = { .reloc_handler = apply_r_riscv_64_rela },
        [R_RISCV_RELATIVE]      = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_COPY]          = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_JUMP_SLOT]     = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_DTPMOD32]  = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_DTPMOD64]  = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_DTPREL32]  = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_DTPREL64]  = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_TPREL32]   = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_TLS_TPREL64]   = { .reloc_handler = dynamic_linking_not_supported },
        /* 12-15 undefined */
        [R_RISCV_BRANCH]        = { .reloc_handler = apply_r_riscv_branch_rela },
        [R_RISCV_JAL]           = { .reloc_handler = apply_r_riscv_jal_rela },
        [R_RISCV_CALL]          = { .reloc_handler = apply_r_riscv_call_rela },
        [R_RISCV_CALL_PLT]      = { .reloc_handler = apply_r_riscv_call_plt_rela },
        [R_RISCV_GOT_HI20]      = { .reloc_handler = apply_r_riscv_got_hi20_rela },
        [R_RISCV_TLS_GOT_HI20]  = { .reloc_handler = tls_not_supported },
        [R_RISCV_TLS_GD_HI20]   = { .reloc_handler = tls_not_supported },
        [R_RISCV_PCREL_HI20]    = { .reloc_handler = apply_r_riscv_pcrel_hi20_rela },
        [R_RISCV_PCREL_LO12_I]  = { .reloc_handler = apply_r_riscv_pcrel_lo12_i_rela },
        [R_RISCV_PCREL_LO12_S]  = { .reloc_handler = apply_r_riscv_pcrel_lo12_s_rela },
        [R_RISCV_HI20]          = { .reloc_handler = apply_r_riscv_hi20_rela },
        [R_RISCV_LO12_I]        = { .reloc_handler = apply_r_riscv_lo12_i_rela },
        [R_RISCV_LO12_S]        = { .reloc_handler = apply_r_riscv_lo12_s_rela },
        [R_RISCV_TPREL_HI20]    = { .reloc_handler = tls_not_supported },
        [R_RISCV_TPREL_LO12_I]  = { .reloc_handler = tls_not_supported },
        [R_RISCV_TPREL_LO12_S]  = { .reloc_handler = tls_not_supported },
        [R_RISCV_TPREL_ADD]     = { .reloc_handler = tls_not_supported },
        [R_RISCV_ADD8]          = { .reloc_handler = apply_r_riscv_add8_rela,
                                    .accumulate_handler = apply_8_bit_accumulation },
        [R_RISCV_ADD16]         = { .reloc_handler = apply_r_riscv_add16_rela,
                                    .accumulate_handler = apply_16_bit_accumulation },
        [R_RISCV_ADD32]         = { .reloc_handler = apply_r_riscv_add32_rela,
                                    .accumulate_handler = apply_32_bit_accumulation },
        [R_RISCV_ADD64]         = { .reloc_handler = apply_r_riscv_add64_rela,
                                    .accumulate_handler = apply_64_bit_accumulation },
        [R_RISCV_SUB8]          = { .reloc_handler = apply_r_riscv_sub8_rela,
                                    .accumulate_handler = apply_8_bit_accumulation },
        [R_RISCV_SUB16]         = { .reloc_handler = apply_r_riscv_sub16_rela,
                                    .accumulate_handler = apply_16_bit_accumulation },
        [R_RISCV_SUB32]         = { .reloc_handler = apply_r_riscv_sub32_rela,
                                    .accumulate_handler = apply_32_bit_accumulation },
        [R_RISCV_SUB64]         = { .reloc_handler = apply_r_riscv_sub64_rela,
                                    .accumulate_handler = apply_64_bit_accumulation },
        /* 41-42 reserved for future standard use */
        [R_RISCV_ALIGN]         = { .reloc_handler = apply_r_riscv_align_rela },
        [R_RISCV_RVC_BRANCH]    = { .reloc_handler = apply_r_riscv_rvc_branch_rela },
        [R_RISCV_RVC_JUMP]      = { .reloc_handler = apply_r_riscv_rvc_jump_rela },
        /* 46-50 reserved for future standard use */
        [R_RISCV_RELAX]         = { .reloc_handler = apply_r_riscv_relax_rela },
        [R_RISCV_SUB6]          = { .reloc_handler = apply_r_riscv_sub6_rela,
                                    .accumulate_handler = apply_6_bit_accumulation },
        [R_RISCV_SET6]          = { .reloc_handler = apply_r_riscv_set6_rela,
                                    .accumulate_handler = apply_6_bit_accumulation },
        [R_RISCV_SET8]          = { .reloc_handler = apply_r_riscv_set8_rela,
                                    .accumulate_handler = apply_8_bit_accumulation },
        [R_RISCV_SET16]         = { .reloc_handler = apply_r_riscv_set16_rela,
                                    .accumulate_handler = apply_16_bit_accumulation },
        [R_RISCV_SET32]         = { .reloc_handler = apply_r_riscv_set32_rela,
                                    .accumulate_handler = apply_32_bit_accumulation },
        [R_RISCV_32_PCREL]      = { .reloc_handler = apply_r_riscv_32_pcrel_rela },
        [R_RISCV_IRELATIVE]     = { .reloc_handler = dynamic_linking_not_supported },
        [R_RISCV_PLT32]         = { .reloc_handler = apply_r_riscv_plt32_rela },
        [R_RISCV_SET_ULEB128]   = { .reloc_handler = apply_r_riscv_set_uleb128,
                                    .accumulate_handler = apply_uleb128_accumulation },
        [R_RISCV_SUB_ULEB128]   = { .reloc_handler = apply_r_riscv_sub_uleb128,
                                    .accumulate_handler = apply_uleb128_accumulation },
        /* 62-191 reserved for future standard use */
        /* 192-255 nonstandard ABI extensions  */
};

static void
process_accumulated_relocations(struct module *me,
                                struct hlist_head **relocation_hashtable,
                                struct list_head *used_buckets_list)
{
        /*
         * Only ADD/SUB/SET/ULEB128 should end up here.
         *
         * Each bucket may have more than one relocation location. All
         * relocations for a location are stored in a list in a bucket.
         *
         * Relocations are applied to a temp variable before being stored to the
         * provided location to check for overflow. This also allows ULEB128 to
         * properly decide how many entries are needed before storing to
         * location. The final value is stored into location using the handler
         * for the last relocation to an address.
         *
         * Three layers of indexing:
         *      - Each of the buckets in use
         *      - Groups of relocations in each bucket by location address
         *      - Each relocation entry for a location address
         */
        struct used_bucket *bucket_iter;
        struct used_bucket *bucket_iter_tmp;
        struct relocation_head *rel_head_iter;
        struct hlist_node *rel_head_iter_tmp;
        struct relocation_entry *rel_entry_iter;
        struct relocation_entry *rel_entry_iter_tmp;
        int curr_type;
        void *location;
        long buffer;

        list_for_each_entry_safe(bucket_iter, bucket_iter_tmp,
                                 used_buckets_list, head) {
                hlist_for_each_entry_safe(rel_head_iter, rel_head_iter_tmp,
                                          bucket_iter->bucket, node) {
                        buffer = 0;
                        location = rel_head_iter->location;
                        list_for_each_entry_safe(rel_entry_iter,
                                                 rel_entry_iter_tmp,
                                                 &rel_head_iter->rel_entry,
                                                 head) {
                                curr_type = rel_entry_iter->type;
                                reloc_handlers[curr_type].reloc_handler(
                                        me, &buffer, rel_entry_iter->value);
                                kfree(rel_entry_iter);
                        }
                        reloc_handlers[curr_type].accumulate_handler(
                                me, location, buffer);
                        kfree(rel_head_iter);
                }
                kfree(bucket_iter);
        }

        kvfree(*relocation_hashtable);
}

static int add_relocation_to_accumulate(struct module *me, int type,
                                        void *location,
                                        unsigned int hashtable_bits, Elf_Addr v,
                                        struct hlist_head *relocation_hashtable,
                                        struct list_head *used_buckets_list)
{
        struct relocation_entry *entry;
        struct relocation_head *rel_head;
        struct hlist_head *current_head;
        struct used_bucket *bucket;
        unsigned long hash;

        entry = kmalloc_obj(*entry);

        if (!entry)
                return -ENOMEM;

        INIT_LIST_HEAD(&entry->head);
        entry->type = type;
        entry->value = v;

        hash = hash_min((uintptr_t)location, hashtable_bits);

        current_head = &relocation_hashtable[hash];

        /*
         * Search for the relocation_head for the relocations that happen at the
         * provided location
         */
        bool found = false;
        struct relocation_head *rel_head_iter;

        hlist_for_each_entry(rel_head_iter, current_head, node) {
                if (rel_head_iter->location == location) {
                        found = true;
                        rel_head = rel_head_iter;
                        break;
                }
        }

        /*
         * If there has not yet been any relocations at the provided location,
         * create a relocation_head for that location and populate it with this
         * relocation_entry.
         */
        if (!found) {
                rel_head = kmalloc_obj(*rel_head);

                if (!rel_head) {
                        kfree(entry);
                        return -ENOMEM;
                }

                INIT_LIST_HEAD(&rel_head->rel_entry);
                rel_head->location = location;
                INIT_HLIST_NODE(&rel_head->node);
                if (!current_head->first) {
                        bucket =
                                kmalloc_obj(struct used_bucket);

                        if (!bucket) {
                                kfree(entry);
                                kfree(rel_head);
                                return -ENOMEM;
                        }

                        INIT_LIST_HEAD(&bucket->head);
                        bucket->bucket = current_head;
                        list_add(&bucket->head, used_buckets_list);
                }
                hlist_add_head(&rel_head->node, current_head);
        }

        /* Add relocation to head of discovered rel_head */
        list_add_tail(&entry->head, &rel_head->rel_entry);

        return 0;
}

static unsigned int
initialize_relocation_hashtable(unsigned int num_relocations,
                                struct hlist_head **relocation_hashtable)
{
        /* Can safely assume that bits is not greater than sizeof(long) */
        unsigned long hashtable_size = roundup_pow_of_two(num_relocations);
        /*
         * When hashtable_size == 1, hashtable_bits == 0.
         * This is valid because the hashing algorithm returns 0 in this case.
         */
        unsigned int hashtable_bits = ilog2(hashtable_size);

        /*
         * Double size of hashtable if num_relocations * 1.25 is greater than
         * hashtable_size.
         */
        int should_double_size = ((num_relocations + (num_relocations >> 2)) > (hashtable_size));

        hashtable_bits += should_double_size;

        hashtable_size <<= should_double_size;

        /* Number of relocations may be large, so kvmalloc it */
        *relocation_hashtable = kvmalloc_objs(**relocation_hashtable,
                                              hashtable_size);
        if (!*relocation_hashtable)
                return 0;

        __hash_init(*relocation_hashtable, hashtable_size);

        return hashtable_bits;
}

int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
                       unsigned int symindex, unsigned int relsec,
                       struct module *me)
{
        Elf_Rela *rel = (void *) sechdrs[relsec].sh_addr;
        int (*handler)(struct module *me, void *location, Elf_Addr v);
        Elf_Sym *sym;
        void *location;
        unsigned int i, type;
        unsigned int j_idx = 0;
        Elf_Addr v;
        int res;
        unsigned int num_relocations = sechdrs[relsec].sh_size / sizeof(*rel);
        struct hlist_head *relocation_hashtable;
        unsigned int hashtable_bits;
        LIST_HEAD(used_buckets_list);

        hashtable_bits = initialize_relocation_hashtable(num_relocations,
                                                         &relocation_hashtable);

        if (!relocation_hashtable)
                return -ENOMEM;

        pr_debug("Applying relocate section %u to %u\n", relsec,
               sechdrs[relsec].sh_info);

        for (i = 0; i < num_relocations; i++) {
                /* This is where to make the change */
                location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
                        + rel[i].r_offset;
                /* This is the symbol it is referring to */
                sym = (Elf_Sym *)sechdrs[symindex].sh_addr
                        + ELF_RISCV_R_SYM(rel[i].r_info);
                if (IS_ERR_VALUE(sym->st_value)) {
                        /* Ignore unresolved weak symbol */
                        if (ELF_ST_BIND(sym->st_info) == STB_WEAK)
                                continue;
                        pr_warn("%s: Unknown symbol %s\n",
                                me->name, strtab + sym->st_name);
                        return -ENOENT;
                }

                type = ELF_RISCV_R_TYPE(rel[i].r_info);

                if (type < ARRAY_SIZE(reloc_handlers))
                        handler = reloc_handlers[type].reloc_handler;
                else
                        handler = NULL;

                if (!handler) {
                        pr_err("%s: Unknown relocation type %u\n",
                               me->name, type);
                        return -EINVAL;
                }

                v = sym->st_value + rel[i].r_addend;

                if (type == R_RISCV_PCREL_LO12_I || type == R_RISCV_PCREL_LO12_S) {
                        unsigned int j = j_idx;
                        bool found = false;

                        do {
                                unsigned long hi20_loc =
                                        sechdrs[sechdrs[relsec].sh_info].sh_addr
                                        + rel[j].r_offset;
                                u32 hi20_type = ELF_RISCV_R_TYPE(rel[j].r_info);

                                /* Find the corresponding HI20 relocation entry */
                                if (hi20_loc == sym->st_value
                                    && (hi20_type == R_RISCV_PCREL_HI20
                                        || hi20_type == R_RISCV_GOT_HI20)) {
                                        s32 hi20, lo12;
                                        Elf_Sym *hi20_sym =
                                                (Elf_Sym *)sechdrs[symindex].sh_addr
                                                + ELF_RISCV_R_SYM(rel[j].r_info);
                                        unsigned long hi20_sym_val =
                                                hi20_sym->st_value
                                                + rel[j].r_addend;

                                        /* Calculate lo12 */
                                        size_t offset = hi20_sym_val - hi20_loc;
                                        if (IS_ENABLED(CONFIG_MODULE_SECTIONS)
                                            && hi20_type == R_RISCV_GOT_HI20) {
                                                offset = module_emit_got_entry(
                                                         me, hi20_sym_val);
                                                offset = offset - hi20_loc;
                                        }
                                        hi20 = (offset + 0x800) & 0xfffff000;
                                        lo12 = offset - hi20;
                                        v = lo12;
                                        found = true;

                                        break;
                                }

                                j++;
                                if (j == num_relocations)
                                        j = 0;

                        } while (j_idx != j);

                        if (!found) {
                                pr_err(
                                  "%s: Can not find HI20 relocation information\n",
                                  me->name);
                                return -EINVAL;
                        }

                        /* Record the previous j-loop end index */
                        j_idx = j;
                }

                if (reloc_handlers[type].accumulate_handler)
                        res = add_relocation_to_accumulate(me, type, location,
                                                           hashtable_bits, v,
                                                           relocation_hashtable,
                                                           &used_buckets_list);
                else
                        res = handler(me, location, v);
                if (res)
                        return res;
        }

        process_accumulated_relocations(me, &relocation_hashtable,
                                        &used_buckets_list);

        return 0;
}

int module_finalize(const Elf_Ehdr *hdr,
                    const Elf_Shdr *sechdrs,
                    struct module *me)
{
        const Elf_Shdr *s;

        s = find_section(hdr, sechdrs, ".alternative");
        if (s)
                apply_module_alternatives((void *)s->sh_addr, s->sh_size);

        return 0;
}